1. Field of the Invention
The present invention relates to a transformer. In the transformer, secondary winding sections are placed in both sides of a primary winding section, all terminals of the secondary winding sections are used as output terminals, and an input terminal is placed in the opposite side to the output terminals. Therefore, a return wire in a high-voltage output side does not need to be provided, and a sufficient insulation separation distance is secured in the relation with a printed circuit board, which makes it easy to implement a circuit. Further, improved efficiency is obtained over a conventional transformer, there is a significant reduction in cost, and products using the transformer can be small in size.
2. Description of the Related Art
Recently, as techniques related to display devices develop, liquid crystal display (LCD) monitors are tending to be widely used in a computer or other display devices. Compared with a CRT monitor, the LCD monitor has an advantage in that the vertical cross-section thereof becomes slim and flickering hardly occurs. The LCD monitor has a fluorescent lamp, which is driven by a high voltage, for a back light system which needs a back-light module.
An inverter including a driving circuit is used to drive the fluorescent lamp. The inverter has a high-voltage transformer, which generates a high AC output voltage from a low AC input voltage so as to supply the voltage to a lamp composing an LCD panel.
The conventional transformer drives one transformer to supply electric power to one lamp. However, in the case where external electrode fluorescent lamps (EEFL) or cold cathode fluorescent lamps (CCFL) are driven in parallel, several transformers are driven to supply electric power to several lamps.
As the LCD TV market or monitor market reaches maturity, the selling price of LCD or monitor decreases, and thus the prices of parts related to a backlight unit decreases accordingly.
Therefore, manufacturers have tried to reduce the number of parts and the unit cost per parts because of this price pressure related to the parts of a backlight unit. As a part of such an effort, attempts to develop a product, in which several lamps can be driven by one transformer, are being made actively.
FIGS. 1A and 2A are plan views of a transformer according to the related art which can drive one lamp, and FIGS. 1B and 2B are diagrams illustrating an equivalent circuit of the transformer.
The transformer shown in FIG. 1A includes a bobbin 100 composed of one primary winding section 101 and one secondary winding section 102, on which a plurality of insulating slits 106 are formed, primary coil and secondary coils 107 and 108 which are respectively wound around the primary and second winding sections 101 and 102, and a pair of cores (not shown) which are inserted into an insertion hole formed inside the bobbin 100.
As shown in FIG. 1A, a primary-side voltage is applied through an input terminal (not shown) formed in the primary winding section 101, and the secondary winding section 102 is provided with two terminals 103 and 104, one terminal 103 being used as an output terminal and the other terminal 104 being used as a ground terminal. Therefore, as shown in the equivalent circuit of FIG. 1B, the transformer can drive only one lamp.
The winding of the secondary coil 108 starts from the output terminal 103 of the secondary winding section 102 and is completed at the ground terminal 104 thereof, thereby causing a return wire 105 to pass through the high-voltage output side. Accordingly, the high-voltage output side and the return wire 105 should be insulated.
In addition, the pair of cores are inserted into the insertion hole formed inside the bobbin 100. In the transformer, an E-shaped core or UI-shaped core can be used, the UI-shaped core being formed by a combination of a U-shaped core forming an outer magnetic path and an I-shaped core forming an inner magnetic path.
As in the transformer shown in FIG. 1A, a transformer shown in FIG. 2A includes a bobbin 100 composed of one primary winding section 201 and one secondary winding section 202, on which a plurality of insulating slits 206 are formed, primary coil and secondary coils 207 and 208 which are respectively wound around the primary and second winding sections 201 and 202, and a pair of cores (not shown) which are inserted into an insertion hole formed inside the bobbin 200.
In addition, a primary-side voltage is applied through an input terminal (not shown) formed in the primary winding section 201, and the secondary winding section 202 is provided with two terminals 204 and 205, one terminal 204 of the terminals being used as an output terminal. Therefore, as shown in FIG. 2B, the transformer can also drive only one lamp.
In the transformer shown in FIG. 2A, the secondary coil 208 is wound in a different manner from the transformer shown in FIG. 1A. That is, the winding of the secondary coil 208 starts from a terminal 203 of the primary winding section 201 and is completed at the output terminal 204 of the secondary winding section 202. Therefore, the transformer has an advantage in that a return wire passing though the high-voltage output side does not need to be provided, which means the insulation between the return wire and the high-voltage output side does not need to be considered.
Furthermore, as in the transformer of FIG. 1A, the pair of cores are inserted into the insertion hole formed in the bobbin 200. In the transformer, an E-shaped core or UI-shaped core can be used, the UI-shaped core being formed by a combination of a U-shaped core forming an outer magnetic path and an I-shaped core forming an inner magnetic path.
FIGS. 3A and 4A are plan views of a transformer according to the related art, which drives two lamps. FIGS. 3B and 3C are diagrams illustrating an equivalent circuit of the transformer, and FIGS. 4B and 4C are diagrams illustrating an equivalent circuit of the transformer.
The transformer shown in FIG. 3A includes a bobbin 300 composed of one primary winding section 301 and one secondary winding section 302, on which a plurality of insulating slits 306 are formed, primary coil and secondary coils 307 and 308 which are respectively wound around the primary and second winding sections 301 and 302, and a pair of cores (not shown) which are inserted into an insertion hole formed inside the bobbin 300.
As shown in FIG. 3A, a primary-side voltage is applied through an input terminal (not shown) formed in the primary winding section 301, and the secondary winding section 302 is provided with two terminals 303 and 304, the terminals 303 and 304 being used as output terminals. Therefore, as shown in the equivalent circuit of FIG. 3A or 3C, the transformer can drive two lamps or one U-shaped lamp to thereby have more improved efficiency than the transformers shown in FIGS. 1A and 2A.
However, the winding of the secondary coil 308 starts from one output terminal 303 of the secondary winding section 302 and is completed at the other output terminal 304 thereof, thereby causing a return wire 305 to pass though the high-voltage output side, as in the transformer shown in FIG. 1A. Accordingly, the high-voltage output side and the return wire 305 should be insulated.
As in the transformers of FIGS. 1A and 2A, the pair of cores are inserted into the insertion hole formed inside the bobbin 300. In the transformer, an E-shaped core or UI-shaped core can be used, the UI-shaped core being formed by a combination of a U-shaped core forming an outer magnetic path and an I-shaped core forming an inner magnetic path.
The transformer shown in FIG. 4A includes a bobbin 400 composed of one primary winding section 401 and two secondary winding sections 402, in which a plurality of insulating slits 405 are formed, primary and secondary coils 406 and 407 which are respectively wound around the first and secondary winding sections 401 and 402, and a pair of cores 408 which are inserted into an insertion hole formed inside the bobbin 400.
As shown in FIG. 4a, the primary winding section 401 is provided with two input terminals 403a and 403b, through which a primary-side voltage is applied. The second winding section 402 is provided with four terminals 404a to 404d, two terminals 404a and 404d being used as output terminals and two terminals 404b and 404c being used as ground terminals. Therefore, as shown in FIGS. 4b and 4c, the transformer can drive two lamps or one U-shaped lamp at the same time to thereby have more improved efficiency than the transformers shown in FIGS. 1A and 2A.
The primary winding section 401 is placed in the center of the bobbin 400, and the secondary winding sections 402 are respectively placed in both sides of the primary winding section 401. In other words, two secondary winding sections 402 are placed in one bobbin, so that one transformer can drive two lamps or one U-shaped lamp.
The winding of the secondary coil 407 starts from the input terminals 403a and 403b of the primary winding section 401 and is completed at the output terminals 404a and 404d of the secondary winding section 402. Therefore, in the above transformer, a return wire passing through the high-voltage output side does not need to be provided, which means the insulation between the high-voltage output side and the return wire does not need to be considered. In general, the transformer is being widely used among transformers according to the related art.
As in the transformers described above, the pair of cores 408 are inserted into the insertion hole formed inside the bobbin 400. In the transformer, an E-shaped core or UI-shaped core can be used, the UI-shaped core being formed by a combination of a U-shaped core forming an outer magnetic path and an I-shaped core forming an inner magnetic path.
However, in the conventional transformers as described above, all the terminals of the secondary winding section are not used as an output terminal, so several lamps cannot be driven at the same time. Therefore, utilization efficiency is considerably decreased, significant costs are wasted, and products using a transformer become large in size.
In addition, the primary and secondary winding sections are placed in a line in one bobbin. The winding of secondary coil starts from one output terminal of the secondary winding section and is completed at the other output terminal thereof. As a result, the high-voltage output side and the return wire should be insulated because of the return wire passing through the high-voltage output side, and a waveform of output current is distorted.
Furthermore, in the case of the transformer in which the input terminal is not placed in the opposite side of the output terminal, a sufficient insulation separation distance cannot be secured in the relation with a printed circuit board which is electrically connected thereto, which makes it hard to implement a circuit.